An initiative of the Sydney Harbour Research Program

A common perception is that cities, and their associated ecological impacts end at the waterline. However, coastal cities such as Sydney are also highly modified underwater.

Below the waterline in Sydney Harbour there is a dense network of coastal infrastructure, the sediments hold a legacy of chemical contamination and shipping activities contribute further stress through antifouling biocides and invasive species.

Healthy estuaries have some natural mechanisms to recover from such stress and much of this is driven by the small invertebrate creatures living on rocky reefs and burrowing through sediments. However, in Sydney Harbour and other urbanised estuaries we have lost many of these important critters, and so have lost their natural capacity for recovery.

Oyster reefs in particular have historically played crucial roles in maintaining healthy estuaries by filtering water, providing habitat for fish and invertebrates and protecting shoreline ecosystems. Centuries ago, estuaries on the south east coast of Australia were packed with intertidal and subtidal oyster reefs, hectares wide. Nowadays, subtidal oyster reefs are mostly absent due to human factors, including the harvesting of shells and live oysters since the 18th century. One of those remnant reefs is located in Towra Point, Botany Bay. The scale of the reef is impressive, but also a sad reminder of what we have lost from other estuaries.

The Sydney Harbour Research Program at SIMS has started a project to restore oyster reefs around Sydney, and to do so at meaningful scales that will rival reefs like the one at Towra Point. Through this project, we focus not only on increasing oyster numbers, but on quantifying the positive feedbacks such reefs can create, including rehabilitation of degraded sediments, improvements in water quality and shoreline protection. We will work, not only for the recovery and resilience of urban estuaries to global change, but also to enhance the socio-economic benefits to the communities that rely on the resources coastal ecosystems provide.

This research is a collaboration between SIMS and the University of Sydney and is generously supported by the Maple-Brown Family Foundation.

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